Neighbors stole from our car?

How would you go about this? Should we do anything or just see if it happens again? So tomorrow’s the super bowl and my Dad has managed to get his day off, which is rare for him. He works a lot of long hours and never has time to relax much. He’s in a good mood, he bought a bunch of things to grill and a big case of beer for him and our guests. He brought the meat in and put it in the fridge, and not even 3 minutes later went out to get the big case of beer from his truck bed. Only to find it empty and open. Obviously hes angry, a case that big was a decent amount of money and he doesn’t feel like going to the store again after a long work day. We know who did it, our neighbors are all older retired people who go on vacation a lot and never really leave there house. Directly across from us, is a house of 3 guys who always have the cops at their door at various hours of the night. They have a clear shot from my Dad’s truck to their front door. I am 99% sure it’s them, and so is my Dad. I want to just let it go because it’d be hard to prove, but I also find it ridiculous we have to worry about things being stolen from right under our nose. This is a pretty nice neighborhood, generally quiet except for the guys across the street. Advice?